Aluminum Bond Jigs

[Hilton Roberts]

We use a lot of aluminum bond jigs to lay up composite parts. We had two bond jigs produced at a vendor who supplied the tools and reports that said the tools were ok. We have had these two tools in house since 2004 and have produced several non conforming parts. Inspection was by-passed and no first article was completed. The two tools are mirror images. We brought the tools into the lab and measured them and the left hand tool is small and the right hand tool is large. We have been able to use high temperature tape to build up the left hand tool until a new one is made.

The vendor says the tools were fine. We took the right hand tool and blued it up and ran the cutter path around it. Sure enough, we took material off....quite a bit in fact.

What I am really curious about is the long term stability of aluminum at a 325 degree cure temperature. Do any of you know if in fact the tools come back to the original size after multiple heat cycles? The bond jigs are about two and a half feet long by two feet wide and about 2 feet high.

Because I did not measure the tool when it was new, I really do not know if the tool has changed or not. I suspect it is not changing but wonder what your experience has been.

My feeling is that if both tools were the same when produced and after two years of service and making both right and left hand parts, that if one tool got large, the other would have gotten large as well. That is not what we have seen.

Chime in and let me know what your experiences have been, please.

Thanks

Hilton

[Matthew D. Hoedeman]

Based on 'common sense', I would have to agree with you in that they BOTH should have exibited the same type of change, even if not to the same degree. They both should have gotten larger or both smaller, not one in each direction.

We don't do that type of work, but I never trust a supplier's certification/calibration/etc. and always do my own, at least enough so that I know what I am using is right. In the case of holding/checking fixtures, I check the net pads and locator pins. I don't use the rest and it is NOT our place to certify the fixture, but how can I use it if I don't know for a fact that at least the locators are correct.

Hopefully this will encourage your bosses to get these kinds of tools into your department before they press them into production. I know you haven;t been there long, so they don't know for sure that you are just about 100% right all of the time, but they will get the idea soon enough. Ya gotta be right to begin with or you'll never get to where you need to be.

[Hilton Roberts]

Matt,

It seems we need to continually re-educate our managers into not trusting everything that comes from a vendor. When I worked in the metrology lab in Saint Louis, one of the first things we did was trash the certs from vendors.

That include Webber and Starrett as far as gage block certs go. We checked each and every block and we started keeping history on those kinds of things from the get go.

Thanks for the response.

H

[#2#]

I'm with Matt and you. If they were going to change I would think they would change in the same direction (larger or smaller) rather than one each way.

As far as stability at temp goes... I would think that at 325ºF(?) that the part wouldn't change much. Of course, it probably depends on section thickness, the time it takes to reach temp. and cooldown times.

[cmmguy]

I have seen ring and plug gages "grow" over time. it was in the couple of tenths range. This usually happened on gages that were made on a RUSH and they were not properly heat treated(I think they skipped the anneally step). These were steel.

It is hard to believe that your fixtures went in different directions. Are these machined weldments? If they are, they might change differently if they were not stress relieved.

But I would bet that they were bad to begin with. Too bad you dont have the evidence to prove otherwise... but still, if they changed, then they were not properly made to begin with.

[Tested]

Were the parts good and the Non-conforming parts just now start?

[Hilton Roberts]

I too have seen gage blocks grow and shrink if the heat treat was not right.

These bond jigs are hogouts. Supposed to have been from the same billet of material. They MAY account for one being large and one small. I think, but cannot prove, the nc program was not mirrored correctly or there were two programs generated to produce the tools.

This long after the horses are gone is too late to find all the dna. The vendor claims the tools were fine and we have 22 ship sets or 44 pieces at 14k apiece.

Pretty soon this is going to add up to real money....

[Wes Cisco]

I too have seen gage blocks grow and shrink if the heat treat was not right.

These bond jigs are hogouts. Supposed to have been from the same billet of material. They MAY account for one being large and one small. I think, but cannot prove, the nc program was not mirrored correctly or there were two programs generated to produce the tools.

This long after the horses are gone is too late to find all the dna. The vendor claims the tools were fine and we have 22 ship sets or 44 pieces at 14k apiece.

Pretty soon this is going to add up to real money....

I would not want to be the person who decided to play with that kind of fire. Even if they trusted the vendor to make them correctly and were really under the gun, a solid first article before allowing production to continue would have limited the damage to ballpark 30K instead of over 1/2 a mil!

[Hilton Roberts]

Wes,

I hear you. The parts are at the high limit of tolerance and that is what causes the problem. We evaluate contour with both PCDMIS and Valisys ( runs in UG ).

Within Valisys, a profile gage may have the 6 degrees of freedom turned off
( TX,TY,TZ,RX,RY,RZ ). This will yield different numbers than it will if Valisys is allowed to best fit the data. The default condition of Valisys is all 6 degrees of freedom turned on.

When this is done, the parts ( measured thus far ) are at the high end of tolerance and are acceptable.

I was aked to report the data with the degrees of freedom turned off and that just caused all kinds of problems.

The contour tolerance of the part in question is +/- .030 inch. I have igesed all the data sets out and imported them into the UG model of the part and put each part on a seperate layer. When I do that and keep the gage restricted to prevent gage float, I can see what the part to part variation is and some of the numbers will blow you away. When you lay up plies of material, a lot of handwork is required and areas where the material is stretched to go around radii is subject to a lot of variation as the plies bulk up and require smoothing.

The up shot is that some of those points vary from part to part to the degree that when the standard deviation is calculated, I am seeing .0179 in. If I assume the process is normal, I am seeing a plus or minus 3 sigma dispersion of .0539 in. That is not at all compatible with an engineering requirement of +/- .030 in.

In order to center the process, something will have to change. Either I get relief on the part tolerances or we adjust the process to center it.

In order to be comfortable the tool produces a good part, I am thinking I need to see multiple parts whose common measured points have a standard deviation on the order of +/- .006 inch or somewhere close to that. Until we do something, we will continue to get what we got and that needs to change.

That is what makes this job so interesting. Always a new dilemma and trying to figure out how to fix it.

[Andrew Gardner]

Here lately, we have made a handful of Bond Jigs for a customer. Every one of them comes thru me before being shipped. I have to supply our customer with point data before they will allow us to ship to them. That way, we are all on the same page.